2018 Vol. 33, No. 9

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Experiment on combustion stability and laminar burning characteristics of biomass gas
2018, 33(9): 2049-2057. doi: 10.13224/j.cnki.jasp.2018.09.001
Abstract PDF(903KB) icon1034 icon803
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In order to gain the combustion stability and laminar burning characteristics of biogas, the laminar flame propagation characteristics of biogas over the equivalence ratio range of 0.7－1.4, the initial pressure range of 0.1－0.5MPa, and the initial temperature range of 290－380K were measured in the constant volume combustion bomb. Furthermore, the main influential factors of the combustion stability and laminar burning velocity of biogas in laminar combustion were investigated. Results showed that the buoyancy instability would appear in the flame propagation process and the flame core would fly upward if the value of the laminar burning velocity was below 0.15m/s. With the increasing of the initial pressure or decrease of the equivalence ratio, the Markstein length decreased and the instability of the flame front increased. However, the effect of the initial temperature on the Markstein length was not obvious. With the increasing of the equivalence ratio, the unstretched flame propagation speed and the laminar burning velocity increased initially and then decreased, and the maximum values were measured at the equivalence ratio of 1.1. Furthermore, the laminar burning velocity of biogas decreased with the decreasing of initial temperature or the increasing of initial pressure.
Heat transfer and condensation of overflow steam in air
2018, 33(9): 2058-2066. doi: 10.13224/j.cnki.jasp.2018.09.002
Abstract PDF(1002KB) icon1017 icon931
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For the heat transfer and condensation of overflow steam in the aircraft steam catapult, a mathematical model was developed to understand the three-fluid flow with the air, steam and condensation water. The module of thermodynamics international association for the properties of water and steam (IAPWS) was incorporated into model system by self-developed user defined function (UDF) code. Eulerian-Eulerian model was used to solve the three fluid flow, exchange of mass, momentum, and energy was included into model equations, moreover, nucleation and growth of liquid droplet were added into mass transfer. Result showed that the mix of the air, steam and condensation water caused the temperature homogenization. Suction volume of steam increased with the decrease of inlet pressure of engine. The condensation phenomena happened with the decrease of steam temperature, and condensation water occurred. Suction volume of steam increased first and then decreased with the increase of air velocity. With the increase of steam velocity, the suction volume of steam increased and the air proportion decreased.
Experiment of combustion characteristic of triple swirler combustor
2018, 33(9): 2067-2073. doi: 10.13224/j.cnki.jasp.2018.09.003
Abstract PDF(841KB) icon1214 icon907
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According to the requirement of low pollution emission of marine gas turbine, the combustion performance of a triple swirler lean premixed combustor was experimentally studied. Results showed that: for the triple swirler chamber, the internal and middle swirl angles determined the success of ignition, and the outer swirl had an influence on the ignition limit. A combination of 10 degrees and 33.3%, 25.0% swirl numbers increase of the inner, middle and outer swirl angles had better ignition and blowout performance. The minimum lean ignition fuel-air ratio was 0.05236, lean blow-out fuel-air ratio was 0.00478; the outlet temperature distribution coefficient was 0.2279, fully meeting the design requirements; the content of NOx was lower than that of 2.62g/kg. But the CO content was higher up to 35.4g/kg, leading to slightly lower combustion efficiency, only 0.9847.
Skeletal chemical kinetic model generation and analysis for combustion of ethylene
2018, 33(9): 2074-2083. doi: 10.13224/j.cnki.jasp.2018.09.004
Abstract PDF(1023KB) icon1296 icon935
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The detailed chemical kinetic mechanism for ethylene was systematically reduced and analyzed using USC(University of Southern California)-Ⅱ mechanism with directed relation graph with error propagation (DRGEP) and path flux analysis (PFA) methods under the wide range of conditions. A skeletal mechanism with 38 species and 243 reactions was achieved from intersection of the two resulting skeletal mechanisms in the first-stage reduction. A skeletal mechanism of ethylene with 30 species and 167 reactions was obtained using sensitivity analysis in the further reduction, and maximum auto-ignition error was 7.10% under the above simulation conditions. This 30 species mechanism showed that, the auto-ignition delay times, laminar flame speeds, temperature and species profiles, brute-force sensitivity coefficients, reaction paths and uncertainty analysis were in good agreement with those of the detailed mechanism. At last, a reduced mechanism including 24 species and 20 global reactions was obtained using the quasi steady state approximation (QSSA) method. This mechanism reproduced satisfactorily auto-ignition delay times, making it more suitably for combustion modeling of engines.
Probe design for measuring total temperature of combustor outlet based on water cooling
ZHAO Kai, LI Feng, LU Fuguo, ZHOU Tao, YANG Hongyu
2018, 33(9): 2084-2092. doi: 10.13224/j.cnki.jasp.2018.09.005
Abstract PDF(291KB) icon903 icon773
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To obtain the outlet temperature of combustor, a kind of high-temperature and water cooling thermocouple was designed. The main factors affecting the results of thermocouple measurement were analyzed after numerical simulation. Results showed that the high-temperature water cooling thermocouple can achieve high temperature measurement under the condition of 2400K. With the increase of the distance between the water cooling structure and the stagnation cover, the temperature measurement result was more accurate, and the increase in the area ratio of the inlet and outlet of the stagnation cover within a reasonable range can make the measurement results more accurate. The surface emissivity of the measuring point had a great influence on the radiation error. The pressure and flow rate of cooling water can be effectively reduced after adding zirconia coating onto the surface of the rake body.
Evaluation of different breakup models and application to the mixture preparation process for diesel engines
2018, 33(9): 2093-2100. doi: 10.13224/j.cnki.jasp.2018.09.006
Abstract PDF(961KB) icon1194 icon771
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On the basis of the theory of jet instability, the turbulent flow inside the nozzle was added into the primary breakup model in the form of weight coefficient.According to the value of deformation of the droplet, the TAB model and the KH-RT model were used to calculate the droplet breakup process by competition mechanism, and then the mathematical model of breakup. The accuracy of the model was verified by comparing the calculated results with the experimental data, TAB and KH-RT breakup model. The maximum relative errors of the Hybrid breakup model for the calculation of the radius and height after impingement were 8% and 6%, respectively, which were far less than the calculated values of the other two breakup models. The three breakup models were applied to the diesel engine, and the effects of these models on the fuel distribution were compared. The study found that the calculation result of the Hybrid breakup model was more accurate than the TAB and KH-RT model.
Simplified mechanism verification of three component surrogate fuels for RP-3 aviation kerosene
2018, 33(9): 2101-2111. doi: 10.13224/j.cnki.jasp.2018.09.007
Abstract PDF(1276KB) icon1331 icon817
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Two schemes were used in mechanism simplification program ReaxRed to simplify aviation kerosene RP-3 semi-detailed chemical reaction kinetics model of three component surrogate fuels. The first scheme used directed relation graph(DRG) method to obtain 109 species and 423 elementary reactions. The second scheme used directed relation graph based on error propagation(DRGEP) method and computational singular perturbation(CSP) method, which obtained 84 species and 271 elementary reactions on the basis of the result of the first scheme. The experimental data of ignition delay of kerosene was adopted to demonstrate the rationality of the simplified mechanism created by the second scheme, the numerical simulation results of laminar flame speed, temperature and mole fraction of important product were compared and analyzed. Results indicated that the second scheme with high calculation accuracy was more economical and practical compared with the first scheme. Under various operating conditions, the average error between the ignition delay time of the second schemes simplified mechanism and the ignition delay time of the semi-detail mechanism was within 6% and their error in the flame propagation speed did not exceed 8%. In order to further verify the simplified mechanism of the second scheme, RP-3 aviation kerosene was adopted as fuel and an experimental study of premixed burner of the Bunsen burner was conducted. The results showed that the numerical calculation results of the simplified mechanism were consistent with the experimental data.
Experiment of transient shock wave focusing performance in two-dimensional concave cavity
2018, 33(9): 2112-2122. doi: 10.13224/j.cnki.jasp.2018.09.008
Abstract PDF(1573KB) icon872 icon805
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Two-dimensional transient shock wave focusing experiment system was designed to investigate the shock wave focusing initiation energy of two-stage pulse detonation engine. Dynamic pressure sensors and particle image velocimetry system were adopted to capture the dynamic pressure of the cavity bottom vertex and the velocity vector field during multi-cycle of shock focus. Furthermore, the cavities of type A and B were used in contrast tests and the velocity vector field was analyed in the meantime. It was found that the first focus was caused by incident shock produced by diaphragm rupture. The post-focus reflected wave formed immediately after shock focus reflected at jet boundary of the nozzle exit and generated the re-reflected wave. The re-reflected wave acted a incident shock in the second cycle and contributed to the second shock focus, then periodic shock focus formed. The focus frequency was up to 7-10kHz. In addition, the velocity field and the strength of the jet weakened with the collision of incident shock waves, then enhanced when high-pressure flow was exhausted, forming a cyclical change.
Influence of equivalence fuel/air ratio on combustion characteristics of internal combustion wave rotor
2018, 33(9): 2123-2128. doi: 10.13224/j.cnki.jasp.2018.09.009
Abstract PDF(732KB) icon1023 icon931
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In order to study the influence of equivalence fuel/air ratio on combustion characteristics of internal combustion wave rotor, the control variable method was used to keep the combustion wave rotor speed and gas filling speed constant by adjusting the fuel injection volume to change of equivalence fuel/air ratio. The experimental investigations on combustion characteristics of internal combustion wave rotor were conducted under different equivalence fuel/air ratios. The results showed that the equivalence fuel/air ratio had great influence on combustion process of internal combustion wave rotor. As the equivalence fuel/aird ratio increased, the combustion wave rotor obtaining combustion pressure gain increased. When the speed of the internal combustion wave rotor was 900r/min, the gas filling speed was 6.741m/s, and the equivalence fuel/air ratio was 1.442, the average combustion pressure gain of the six working cycles was up to 246.29%. The flame propagation velocity was similar to normal distribution with the change of equivalence fuel/air ratio, which reached a maximum 10.8m/s around the stoichiometric ratio. Under the condition of equivalence fuel/air ratio less than 1, the flame front was inclined downward, and the flame front was inclined upward in the case of the equivalence fuel/air ratio was greater than 1.
Numerical analysis of aerodynamic damping for centrifugal impeller
2018, 33(9): 2129-2138. doi: 10.13224/j.cnki.jasp.2018.09.010
Abstract PDF(1295KB) icon911 icon11
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In order to carry out the numerical analyses of the flow fields with moving boundaries in centrifugal impellers, the codes for the grid deformation and the unsteady flow simulations were developed independently, by which the calculations of the aerodynamic damping of centrifugal impellers were realized. By adopting the compactly supported radial basis function to carry out the data transfer of surface deformation from the structure mesh to the flow mesh, and utilizing the binomial tree technique to fulfill the wall distance calculations, the computation efficiencies of grid deformation and flow-field analyses were greatly increased. According to the test cases of an oscillating cascade and a centrifugal impeller, the correctness of the code for the simulations of the flow-fields with moving boundaries and the flows in centrifugal impellers was validated. Then taking a centrifugal impeller as the research object, the calculations of modal aerodynamic damping ratios were carried out. Results showed that, the aerodynamic damping ratios of two selected modes were both positive. The modal aerodynamic damping ratio had no relationship with the oscillating amplitude under small oscillations. For the disk vibration mode, the value of aerodynamic damping ratio decreased as the operating condition shifted towards the stall point.
Analysis and control of tip-leakage vortex core stability of turbine rotor
2018, 33(9): 2139-2149. doi: 10.13224/j.cnki.jasp.2018.09.011
Abstract PDF(1609KB) icon1261 icon964
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The feature of tip-leakage vortex breakdown and the stability mechanism were analyzed and summarized using the first-stage rotor blade of GE-E3 turbine. The study indicated that: the breakdown of tip-leakage vortex core was caused by vortexs centrifugal instability; the vortex core expanded rapidly after losing stability and reversed flow was formed; the vortex core stability depended on two factors: swirling number and reversed pressure gradient. After that, the control of tip-leakage loss was carried out from the perspective of vortex core stability. Calculations show that: moving forward the loading of tip blade profile can reduce the pressure gradient; employing straight profile on the suction surface after passage throat can directly decrease the profile diffuse factor; and the redesigned blade by those two methods can obviously weaken the tip-leakage vortex, suppress the instability of vortex core and decrease the tip-leakage losses.
Coherent structures of cascade under different attack angles with DMD method
2018, 33(9): 2150-2160. doi: 10.13224/j.cnki.jasp.2018.09.012
Abstract PDF(1371KB) icon942 icon571
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In order to analyze the characteristics of coherent structures of unsteady flow in a cascade separation flow, the large eddy simulation of single channel cascade with three different attack angles was carried out. Moreover, dynamic mode decomposition was made to analyze the inherent structures of the three different operations. With DMD(dynamic mode decomposition) method, the complex temporal-spatial flow fields can be decoupled and the coherent structures of different frequencies and scales can be captured. Besides, the main frequencies and their structures can be got to reflect the main dynamic behavior. Moreover, with DMD method, thousands of different flow fields can be expressed by low dimension of only dozens of modes. With the application of DMD method, the results showed that instability shear vortex was generated by flow separation of the leading edge of the cascade, coupling with the shedding vortex in the wake zone, producing new coherent structure. When the attack angle became larger, the shear vortex and its interaction with shedding vortex were strengthened, making the flow field more complicated.
Body force model for multistage axial compressor-three-dimensional application
2018, 33(9): 2161-2169. doi: 10.13224/j.cnki.jasp.2018.09.013
Abstract PDF(1231KB) icon1004 icon597
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The time-marching three-dimensional computational model based on the body force model was used to obtain the general characteristics and flow field of a single-stage transonic compressor with circumferential total pressure inlet distortion. Comparison between calculated and related experimental results was made to verify the accuracy and reliability of the model. Then the internal flow field of a four-stage low speed axial compressor with circumferential total pressure inlet distortion and twin swirl inlet distortion were analyzed in detail respectively by this model. The relative error between the calculated results of the single-stage transonic compressor and the related experimental data was less than 2%, and the distribution of the internal flow field agreed with the experimental measuring data. The calculated results of the four-stage low speed axial compressor reflected that the circumferential total pressure inlet distortion worsened the aerodynamic performance and stability of the compressor while the twin swirl inlet distortion had limited impact. Meanwhile, the travelling process of inlet distortion with different forms in the multistage axial compressor was also revealed. The results fully prove that the model has bright prospects of application in the field of inlet distortion.
Numerical analysis of effect of gas-solid coupled design on oblique impeller performances
2018, 33(9): 2170-2177. doi: 10.13224/j.cnki.jasp.2018.09.014
Abstract PDF(1078KB) icon781 icon603
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A one-way three dimensional gas-solid coupled design method was proposed to obtain the optimized performance blade profile at the design point. The original thermal state blade profile (denoted as RT) designed by the aerodynamics was used for calculating the flow field characteristics and deformation through one way coupled method. Then two revised cold state blade profiles with and without casing treatment (denoted as RC and RC-tip) through an area-averaged 3D interpolation modeling method were obtained. Results indicated that the flow rate of RC-tip impeller at choke point improved 1.93% under designed speed. The minimum blade loading also dropped by 30%. At low speed, performance of RC-tip was obviously better than that of RT, proving that the coupled design method optimized the blade loading and flow capacity of oblique impeller.
Improved slip factor model for centrifugal compressor
2018, 33(9): 2178-2187. doi: 10.13224/j.cnki.jasp.2018.09.015
Abstract PDF(1064KB) icon959 icon598
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An improved slip factor model based on Qiu model for centrifugal compressor was developed. A secondary flow term was added to the Qiu model to correct the slip factor. Furthermore, the difference between the exit blade angle and the maximum blade angle as well as the corresponding position was taken into account. The improved model was verified by CFD with subsonic impeller Krain4, transonic impeller Krain6 and IET200 impeller. The constant coefficient c of the secondary flow was discussed. Compared with the CFD results, there as small error of the improved model. Results showed that compared with Qiu model and other traditional slip factor model, the improved model had higher accuracy, and the average relative error was below 2%. This improved model is suitable for subsonic and transonic centrifugal compressors.
Material characteristics of mechanical seal in shaft end of aviation kerosene pump
2018, 33(9): 2188-2197. doi: 10.13224/j.cnki.jasp.2018.09.016
Abstract PDF(1336KB) icon786 icon551
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In order to select the mechanical seal materials suitable for working in aviation kerosene, the frictional characteristics of these materials were studied. Through the friction-wear tester, the friction coefficients and the temperature rise of materials were obtained under different working conditions and surface roughness. The microscopic wear morphology was observed for three groups of typical matching materials under the atomic force microscope(AFM). The differences between abrasive wear and adhesive wear were analyzed, and the key parameters of wears were calculated. It found that, when the conditions were set, polytetrafluoroethylene (PTFE) was the best soft material, and the hard materials got the best friction performance when their surface roughness equaled 0.05. Besides, different materials had few differences in their performance. It also found that PTFE caused the least amount of element migration on hard surface which, in turn, caused the smallest single abrasive grain grooves. The adhesive wear caused the migration of surface height distribution function. In addition, the adhesive volume and average adhesive thickness were inferred by discretization solving formula.
Locating the crack tip algorithm based on displacement field
2018, 33(9): 2198-2204. doi: 10.13224/j.cnki.jasp.2018.09.017
Abstract PDF(824KB) icon978 icon625
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An algorithm of locating the crack tip based on displacement filed around crack tip was proposed. Give the problem of locating the crack tip,the solution was tured to solving the minimum value by building the objective function including crack tip location firstly. And then the location of crack tips was assumed in a format of mesh, nonlinear optimal problem can be analyzed through a linear least squares approach after an assuming crack tip was chosen. The exact crack tip was gotten by iterative analysis. The results show that this algorithm has converged to the Ⅰ-mode and Ⅰ-Ⅱ mix-mode exact crack tip during four iterative steps in six seconds. The algorithm can provide technical assistance for crack measurement technique and has high engineering values.
Initial research on impacts of maneuver loadson core engine tip clearance
2018, 33(9): 2205-2218. doi: 10.13224/j.cnki.jasp.2018.09.018
Abstract PDF(1468KB) icon873 icon605
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Based on a typical aircraft engine, the calculation model was built by studying model simplification methods and analyzing main loads and loading procedures in maneuver flight. By grasping the change rule of radial tip clearance subjected to different kinds of maneuvering loads by finite element simulation, it can provide significant reference for studying the effects of tip clearance variation on aero-engine performance. Discovered by rational analysis on the distortion of cases and rotors in consequence of gyroscopic moment and normal overload, it can be concluded that two kinds of loads can cause distinct deformation in the core engine. The mean of the relative variation of radial tip clearance subjected to gyro moment was up to -2.174, while the value subjected to normal overload was up to -1.572 owing to the weaker influence of normal overload. Consequently, the impacts of maneuvering loads on engines cannot be ignored when studying the radial tip clearance variation.
Influence of stator wake on aeroelasticity of rotor blade
2018, 33(9): 2219-2227. doi: 10.13224/j.cnki.jasp.2018.09.019
Abstract PDF(1180KB) icon951 icon669
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An energy method was proposed to consider the effect of the wake induced by the upstream stator on the aeroelasticity of the rotor blade based on the phase lagged method, and then validated by the time-marching method. The effects of wake on aerodynamic damping of rotor blades under different modes and interblade phase angles were investigated. The results showed that the wake had a significant effect on the aeroelasticity of the rotor blades, and can be simulated by the developed method accurately and efficiently. Compared with the first torsional mode, the wake had a more serious impact on the aeroelasticity of the first bending mode. Furthermore, for different interblade phase angles, the wake can weaken the low aerodynamic damping and strengthen the high damping for the first bending mode, in contrast to the first torsion mode.
Application and comparative analysis of orthogonal polynomials inuncertain rotor dynamic response calculation
2018, 33(9): 2228-2234. doi: 10.13224/j.cnki.jasp.2018.09.020
Abstract PDF(695KB) icon983 icon598
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In order to quantify the influence of interval uncertainties on the dynamic response of a rotor system, a non-intrusive interval analysis procedure was proposed using orthogonal polynomials, so the strict requirements of probabilistic distribution in stochastic methods were met. The deterministic model and equations of motion were established via the finite element method. The surrogate models of the uncertain response were derived by using Chebyshev polynomials and Legendre polynomials and the general solution procedure was illustrated. The classic Monte Carlo simulation was used to demonstrate the accuracy and efficiency of the two series based interval methods. Compared with the results of Monte Carlo simulation with 500 samples, the errors in the interval methods were less than 1% and the computing time were 2.5% and 5.4%, respectively. In the problem under study, the Chebyshev polynomials based method was more efficient. Then the dynamic response curves of the rotor under different uncertain parameters with different uncertain degrees were given. The results show that the orthogonal polynomials can be successfully applied to uncertain rotordynamics with high efficiency and accuracy. Uncertainty has significant effects on the dynamics of the rotor system and multiple uncertainties propagation may lead to heavy vibration.
An Wiener process perfermance degradation model with two transformed time scales function
2018, 33(9): 2235-2241. doi: 10.13224/j.cnki.jasp.2018.09.021
Abstract PDF(607KB) icon1104 icon603
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A Wiener process degradation model with two transformed time scales is proposed for reliability assessment based on products deterioration information. The maximum likelihood estimation (MLE) for model parameters is constructed. Then the failure time distribution (FTD) is derived, the reliability and life can be inferred accordingly. A comprehensive Monte Carlo simulation study and a real application have been conducted, and the widely adopted Wiener process model with mixed effects is adopted as a reference for a better understanding. According to the definition of the 10th degradation percentile curve, comparative results illustrated that the proposed method can effectively improve the reliability assessment precision. Regarding further lifetime assessment, the median life derived from the proposed method was 232.9h smaller than that derived from the referenced method, and the 10th failure time distribution percentile was 109.4h. This showed that the results from the reference method were more dangerous in practical engineering.
Effect of movable flat baffles plenum volume on pressure distortion flow field of engine
2018, 33(9): 2242-2247. doi: 10.13224/j.cnki.jasp.2018.09.022
Abstract PDF(809KB) icon1180 icon588
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Based on the effect of movable flat baffles plenum volume on inlet pressure distortion flow field of engine, the destabilization characteristic of the movable flat baffles plenum volume on small flux tube engine air flow field was obtained. Through the process of problem discovery, analysis, numerical simulation, improved design, and test verification, the movable flat baffles plenum volume was proved in reducing the distortion intensity of inlet pressure flow field, and the engine of less than 200mm diameter flux tube was covered within the range of effect. In order to avoid destabilization to the inlet air flow field of the movable flat baffles plenum volume, corresponding measures should be taken to reduce the volume in the design of the pressure distortion device.
Linear stability of confined mixing layer
2018, 33(9): 2248-2256. doi: 10.13224/j.cnki.jasp.2018.09.023
Abstract PDF(1138KB) icon968 icon567
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Linear stability analysis was utilized to investigate the stability characteristics of a supersonic boundary/mixing layer confluent flow. The basis flow was designed as a mixing layer with hyperbolic-tangent profile over a compressible boundary layer with similar solution profile. Special attention was paid to the influence of wall distance and convective Mach number on the stability of this field, of which adiabatic wall condition was used. The distance from mixing layer center to the wall ranged from 5 to 15 times boundary layer thickness, and the convective Mach number varied from 0.6 to 1.2. It was found that novel multi-unstable modes existed in the confluent flow and the dominant modes showed different manners with varying wall distance and convective Mach number.
Reversal design of external compression bump of Bump inlet based on osculating cones principle
2018, 33(9): 2257-2267. doi: 10.13224/j.cnki.jasp.2018.09.024
Abstract PDF(1270KB) icon981 icon542
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A method for the design of external compressed bump of Bump inlet based on the theory of osculating cones was proposed.. A variable was introduced to control the shape of bump so that the pressure gradient on the bump surface can be adjusted. In this way, the incoming boundary-layer can be further damped. Meanwhile, a quick mass flow coefficient estimation was set up in accompany with the design process to evaluate the mass flow coefficient of the Bump inlet. The discrepancy of the mass flow coefficient estimation was less than 2%, validating the accuracy of the estimation. Results showed that osculating method can generate more extensive bump configuration, which can enhance the mass flow coefficient by 4.03%, and disperse additional boundary layer flow by 2.12%.
Design approach and experiment of three-dimensional over/under TBCC exhaust system
2018, 33(9): 2268-2277. doi: 10.13224/j.cnki.jasp.2018.09.025
Abstract PDF(1250KB) icon934 icon508
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To design a three-dimensional turbine based combined cycle (TBCC) exhaust system, a design approach was presented. It employed osculating method based on flowfield of nozzle with optimum thrust to design a three-dimensional section controllable dissymmetric ramjet nozzle. And on the basis of curved ramjet flowpath, a new scheme of rotating and sliding the shared surface was proposed to regulate the throat area of the turbojet nozzle. Cold flow experiments and numerical simulations were conducted at typical test points. The comparison proved that the design approach of TBCC exhaust system is practicable. Under the ramjet mode, the comparison of static pressure distributions showed agreement and the relative root mean square error was less than 10.8%. Under the other modes, obvious deviations appeared in the area where the shock wave interacted with the boundary layer, the maximum relative error was 30.6%. However, the variation tendencies of the static pressure distributions were consistent.
Numerical study on boundary layer suction at throat of a CARET inlet
2018, 33(9): 2278-2284. doi: 10.13224/j.cnki.jasp.2018.09.026
Abstract PDF(867KB) icon800 icon494
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To control the flow separation of a CARET inlet, the boundary layer suction slots at the throat of the inlet were designed. The commercial CFD software Fluent was used to simulate the flow field at the design point (Mach number of 2.0). Total pressure recovery and distortion at exit of inlet were used to evaluate the effectiveness of different devices. Simulation results indicated that boundary layer suction in throat can fix the normal shock in the throat and form a stable flow field. It can weaken the shockwave/ boundary layer interaction, suppress flow separation, remarkably increase the total pressure recovery and reduce the total pressure distortion at exit surface of inlet. The front placing slots at the throat section can decrease the distortion of exit surface obviously compared with a rear position. As the suction mass flow increased, the inlet performance firstly became better, and then leveled off.
Aeroengine gas path parameter prediction based on dynamic ensemble algorithm
2018, 33(9): 2285-2295. doi: 10.13224/j.cnki.jasp.2018.09.027
Abstract PDF(1118KB) icon792 icon553
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For the problem that single global modeling methods cannot get satisfactory aeroengine gas path parameter prediction results, ensemble algorithms with a combination method called dynamic weighted kernel density estimation(DWKDE) were proposed.Neighboring samples of the test samples were chosen.The weights of the base learners were dynamically calculated by evaluating the base learners' local performance in the neighboring samples. Based on the calculated weights, the integrated prediction of the time series was realized by the weighted kernel density estimation. The proposed combination method was insensitive to outliers and deviations from normality. Applying this combination method to AdaBoost.RT and AdaBoost.R2, experiments were conducted on gas path parameters of aeroengine, verifying that the proposed algorithms can achieve higher prediction accuracy than the single neural network and the traditional ensemble learning algorithms, for example, the root mean square error(RMSE) can be reduced by at least 27%.
Method for designing constant thrust power schedule
MIAO Keqiang, WANG Xi
2018, 33(9): 2296-2304. doi: 10.13224/j.cnki.jasp.2018.09.028
Abstract PDF(537KB) icon641 icon576
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In order to make the power level angle (PLA) have the same bijection relationship with the thrust when the environment changes before operational limit exceedance, and ensure the pilots ability of unrestricted throttle movement as well as the safety of the engine, a method used to design a constant thrust power schedule was proposed. The research was based on a simulink turbofan engine model and the results were organized as look-up tables in different structures with limitations. Simulation was done to confirm the validity and demonstrate the effectiveness of the schedule obtained with the approach. The constant thrust takeoff schedule, constant thrust idle schedule and constant thrust part power schedule with the present constant thrust control (CTC) method were proved to be valid. The results can be applied to this specific engine but the method can be applied to any areoengine and can be even extended to the unmanned plane.

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